Should the US Adopt Metric Standards?

Seven years ago, Robert Lipsett, engineering manager at Danaher Motion, wrote a Design News blog about the dwindling reasons for the US to remain wedded to nonmetric standards. Surprisingly, this blog post received no comments for or against. But the need remains for the US to finally jump to the metric system, and I bet it wouldn't take as long for us to adopt metric units as some skeptics think.

Canada, our largest trading partner, adopted metric standards in the 1970s, although commercial relations with the US still require the use of some English units for many products that cross the border. I have traveled to Canada many times, and I found it easy to adapt to the use of grams for product weights, liters for gasoline purchases, and kilometers for distance. Kilopascals for pressure take a longer adjustment, but how often do we think about barometric weather readings? Perhaps the use of metric units in college and grad school makes them more familiar to us engineers and scientists.

The US exports products worldwide, so many manufacturers already use metric fasteners and measurements. Semiconductor suppliers provide device-package specifications in metric and English units, and even kitchen measuring cups and measuring spoons come marked with metric and English units. And consumer products include metric and English units. So a complete switch to metric units wouldn't require much effort -- just a bit more attention to measurements we already see.

Metrication wouldn't immediately cause a wholesale switch to millimeters and meters from feet and inches. In Canada, for example, I can still buy an eight-foot 2 x 4 and a six-inch-wide piece of siding. Here in the US, we could still buy screws sized as 6-32 or 10-24, though more products would use metric threads and sizes. Many of the machine tools I use already have metric designations, and I have a helpful conversion chart for those that don't.

US residents already use mixed units such as x milligrams of caffeine per ounce of cola drink and y grams of fat per serving of, say, cookies. The standard method for sizing tires combines millimeters (for tread width) with inches (for rim diameter). Tire inflation for a typical passenger car is 30psi, which is also given in its metric equivalent (207kPa, or kilopascals). Light bulbs use eighths of an inch for bulb diameter and full inches for fluorescent tube lengths, but the socket is always measured in millimeters.

So metrication creeps forward in the US, but it's time to make the last 100-meter run and, to borrow Nike's slogan, just do it.

Do you agree with Jon? Tell us your opinion in the comments section below.

I vote that we move to metric. I found my sons thinking in metric. They were driven by their science courses. I was too, when I was young (oh, so long ago). It makes no sense to stay with such an antiquated system as we have now. When I did work for NASA the excuse was that they didn't want to have a period of confusion. That made no sense, as they had working for them a lot of smart people. Most of these would have lots of exposure to the metric system through their science and engineering education. Now, with all the international efforts in space it makes less sense. Standardization on a more rational system will be a good thing for the US. This is one good thing that came out of the French Revolution. Let's get on board.

I have to agree. Americans have had enough exposure to the metric system through travel, markings on consumer goods, and schooling. Both systems are being taught in elementary schools without any fanfare while those of us in the technology sector easily work back-and-forth on a daily basis. Interestingly enough, it would not take an act of congress to make the change. According to a reference I read many years ago, use of metric measurement system "for commerce" was already approved by congress in 1866. Time to move forward.

In 1970, everyone writing in trade magazines, such as this one, was in agreement that metrification was happening now. Even the Cincinatti Reds marked their outfield wall distances in meters, with feet as a secondary unit. Well, a small amount of metrification occurred in the next 15 years or so as I remember having to buy metric wrenches for my 1985 Chevrolet. For the alternator and another driven accessory, I still needed 1/2" and 9/16" wrenches though. Now, it seems that our automobile industry has completely metrified. My company supplies industrial bearings to both end users through distribution and OEMs directly. Talking with the former, we speek in inches and pounds. With the latter, it's millimeters, kilograms and Newtons. The Thyssen-Krupp company has opened two steel mills on Mobile Bay, Alabama, and they have dictated 100% conformity to metric units. This was extended to sub-contractors, who were not allowed to use adjustable crescent wrenches during construction of the mills.

TJ, the units are not the only potential pitfall. When I first started programming satellites, we were given the lecture about telemetry. Specifically, we were told to pay attention to the sign of the numbers and the endian-ness of the numbers. Evidentially there was a satellite where the mistake was made and the programmer shot the craft into deep space instead of putting it into a stable orbit.

Long before the French developed the Metric system, the British had theirs. They built a huge level of commerce around it. The US continued with that system, slightly modified and it still remains to this day.

Much of the US system was worked up around carefully developed rules of thumb. The metric system was not. It was developed from arbitrary fundamental scientific units that had little relation to much of anything. Take the original definition of the Meter: It was based upon a ten millionth of the meridian from the pole to the equator through Paris.

That's not a particularly useful number. The Nautical Mile was based upon the Mercator Projection and it was intended to be about 1 minute of arc along any meridian. To this day, pilots and mariners still use this approximation.

From a practical perspective, the standard units were intended to be commonly used. The Metric system, well it fell wherever it fell.

The Metric system is based upon the notion that everyone has ten fingers. But a much more realistic system would go binary. 1/2, 1/4, 1/8, 1/16, 1/32...

This gets you exactly the precision you measured, not some ideal number plus or minus some slop.

The reason why the standard system is still here is because it was meant to be used without a calculator. Nobody thinks much about how it came about and how arbitrary the metric system really is.

We still use degrees. Does anyone use Grads? We still use millibars, does anyone use kPa for the weather?

The metric system was not meant to be used by mortals. It gives the illusion of precision whil the units are actually impractical as can be.

But I guess in this day and age, where mental computation seem as outmoded as a slide rule, Where measurements are made automatically by machine, those older systems "don't make sense." Go figure...

ab3a, I understand where you are coming from, but I cannot agree with you. The units like nautical miles are really not used by most of us. Even if the polot is using them, the passengers see statute miles on their display for example. Actually, the foot and yard are fairly arbitrary as well as the meter. Should we go back to the cubit?

When I was living in England a few years ago, there was a scandal becuase food vendors were being forced to switch to metric. The argument used was the one you use, about being able to easily split things in half, then in half, etc. That is fine when there is no technology, but these same vendors had electronic payment decvices in their shops.

I always found it easier to calculate complicated things in my head (such as area and volume) with the metric system. Frankly, it is the same reason we picked a decimal currency system.

Pilots have to deal with mixed measurement systems as a matter of course, but at least the systems don't need to relate to each other. Speed and distance are in knots, altitude is in feet, temperature is in Celcius, you get the idea.

Many of the arguments about why the metric system is more expensive or more difficult are specious. The problems come from dual systems. Sure, for now, metric materials are more expensive to obtain in the U.S. But, that's because we still mostly use imperial. It costs extra to mill and inventory the smaller quantities of "special" sizes. If we were metric, those economics change.

One poster commented that Canada still largely uses imperial units in construction materials. Isn't it possible that happens because the U.S. buys a lot of material from Canada and vice versa? Easier to maintain one inventory. If the U.S. really went metric, I'd bet that Canadian lumber would be in millimeters too.

I recall back in the 70s the push to convert to metric. From what I remember, the main objectors were the automotive and aircraft industries, based on the cost of materials and even more, tooling. Tooling wears out. Most of it has been replaced many times since then. Materials are less expensive if they are all based on one system, especially in a global market. Now, the automotive industry has changed over. In contrast, Boeing has supposedly suffered huge monetary losses and months of delays on the 787 program, in part because of the difficulties in maintaining a global supply chain for an aircraft designed in imperial units.

The bigger problem isn't the arbitrariness of one system or another, it is the existence of dual systems, with dual supply chains, and conversion factors. One of the complaints from many people back in the 70s was that the metric system isn't easier, it's harder...because you have to remember so many conversion factors and multiply everything to figure out how much of something there is or how big it is. That's the cost of not just switching over, as Australia did. Get used to how big a centimeter is. Get used to how much is in a liter. Get used to how much a gram or a kilogram weighs.

I can never remember how many tablespoons in a cup, or how many cups in a quart, or a gallon, even though it's largely binary. On the other hand, it is really easy to figure milliliters to liters. I can easily envision how much a kilogram weighs because I know about how big a 10cm x 10cm x 10cm cube is, and what that amount of water weighs. How much does a gallon of water weigh? How many gallons in a cubic foot? How much does a cubic foot of water weigh? How many foot-pound-seconds in a horsepower?

Units we don't use often might take a little longer to get used to. Even though the definitions are obvious, I've never been able to internalize foot-pounds as work or foot-pound-seconds as energy, unless I stop to think about lifting something a foot in a second. But, I know about what a Watt and a Joule are. They are just the units I'm used to.

I know 30psi or so is about the pressure in a car tire. Twice that is the tire pressure in a trailer tire or what an air wrench runs at, half is about standard sea-level air pressure. But, I also know that sea level is about 100kPa, car tire pressure is about 200kPa, the air wrench runs at about 400kPa, and so on. It is about developing internal references, not how arbitrary or complicated the system is.

The faster we switch make the change, the less it will cost and the faster people will get used to it.

Canadian lumber is sold in metric units, but most stores also give the equivalent in the normal inches and feet. So you can buy an 8-foot 2x4 or the same lumber with metric units. Just about everything else is metricized.

One of my favorite / least favorite subjects We really are at a disadvantage in the US. I used to work for a German company. I loved the drawings and all of the metric hardware. It was so simple, most of the dimensions were in multiples of 10. You could do the math in your head. But, now try to design in the US with off the shelf raw material in millimeters. There is no 10 millimeter plate, okay let's use 3/8" thick, but wait that's 9.525 mm. The design is off to a bad start already. Until, the raw materials become metricized we will still be behind the eight ball. I don't see that happening anytime soon. And pipe, that's another can of worms, but the EU has never fully metricized theirs either, so don't feel too badly about that.

We recently switched to metric units at my job. But very few people have internalized the metric system, and most of us still need to convert dimensions into inches in order to think about them practically. For stress calculations, I've found that some of my co-workers convert all of the units into inches, calculate the stress in psi, then convert back to MPa.

On the other hand, my kids grew up in El Salvador, and tend to think mostly in metric units. I think the increasing diversity of the U.S. population is one factor that will help push us along the path towards the metric system.

Jon, thanks for taking up this subject again. Seems like I've been seeing this discussion come and go for most of my life, and I keep wondering why we haven't adopted this set of standards. At minimum, we should be using both. If we do that for a generation or so, making the switch to metric would be less painful. I agree with Dave, increasing diversity in the population will help push us toward this goal.

It seemed like the US was ready for the switch in the Seventies, but Congress just couldn't force the change. We are somewhat reluctant to change in any form, just look at the huge expense in using paper dollar bills. We have stacks of coins minted and ready to go, but the masses aren't ready to change.

I believe that in the Carter administration we did "switch" to metric. The Reagan administration later abandoned it. That is when all of the car makers made the switch, and they didn't bother to "switch" back after Reagan repealed the Carter initiative. (That's the way I remember it anyhow.)

I checked myself - it was actually Ford: (from some article)

"Gerald Ford signed the Metric Conversion Act on December 23, 1975"

"The 1975 Act didn't last very long. You can imagine that American scientists, who had long been using metric units to describe their work to others in the international scientific community, were excited about the conversion.A Metric Board was created by the law to oversee the switch, complete with PSAs and jingles about metric measurements. But your parents and mine decided they weren't in the mood to learn anything new that decade, and public opposition the process of officially converting to the metric system (called metrication). The result was a law passed under Reagan that repealed the metrication in 1982."

But, if the US goes metric, what will I do with all the unit conversion apps that I've grown accustomed to?

In my job, metric is already king. English units offer me nothing other than inconvenience and confusion (for compound units). My material and component selection tasks would be easier if all suppliers included metric parameters by default.

I agree, metric all the way! (but I don't need the government to tell me which side of my ruler to use...)

Ford may have initiated it, Ttemple, but Carter pushed it. And I remember he was ridiculed for it. When Reagan ditched it, I remember people saying it was one more dumb Carter idea down the drain. There is a good portion of the U.S. population that prides itself on keeping its old habits.

Jon, you are "Spot-On". The switch has already been made; if only subliminally. Like anything, waiting for the "official" launch shouldn't affect your own personal efforts. "Switch" to the Metric System-? We already have. Don't you think synonymously in length now-? (Hmmm ... .030"... that's 3/4mm ...) Don't you have two sets of socket wrenches-? A digital caliper that switch-toggles the LCD from English to Metric-?

As you pointed out, as scientists and engineers we were subject to thinking "metric" in college, and just never switched it OFF. I liken this integrated thought process of English/ Metric to the language here in South Florida, where the huge Latin population has presence on TV networks, Billboard and Radio. Commonly referred to as "Spanglish" the language here crosses the cultures. I look at English/Metric the same way. Maybe we can coin a phrase here: Metglish, or perhaps Englic!!

The only way is to do it by government edict, in the way South Africa and Rhodesia did in the 70's. After such-and-such a date everything will be made in metric. Imperial measurements will no longer be taught in school. Old equipment can be maintained but all new equipment will be metric. S.Africa went further and banned the importation of imperial measuring equipment.

I have done a couple of science classes here in the US and it always amazes me how 'conversions' are taught and seen as a very abstract concept. One prof got all annoyed when I pointed out that mixing units(sq metres/acre) was not standard.

However, it takes years to clean out 'imperial'. In the 80's a fellow apprentice fitter- and-turner was happy because he had been given a set of imperial micrometers. If you make imperial size parts make them in imperial - conversions(either way) are never the same.

Here in the US we brought in some European equipment. We had to fabricate mold plates locally. Our machinists insisted on converting to inches(on CNC machines). 80 plates later, and all 1/16" too short I was free to say 'I told you so'.

Jon, it's very important to use international metrics/standards in business, especially with other countries, otherwise conversion from one unit to other is a problem. For domestic purposes, if we are using our own metrics and standards, nothing going to be happen because both the seller and buyer are following the same metrics.

I agree, Mydesign. As others have commented, though, some metric standards can cause confusion and a later comment noted metric "standards" for O-rings have problems. I never knew so many O-ring diameters and sizes existed. I wonder if there is a way to also note the O-ring materials.

Jon, while I am travelling in US and UK, most of the time I get confused with these types of metrics. In my country we are following Kilometers, gram, cm and second. When I first landed in US, the taxi driver talked me about distances in miles and weight in pounds, I got confused. This may be true with all travelers, who are following different metric systems in their home land.

As far as I know, the UK and the USA are the only two backward countries to remain non-metric in everyday life. All science and most engineering is metric already. The funny thing is, the UK and USA cannot even agree on units - US gallon is 3.8 litres and the UK gallon is 4.55!
The US claims "a pint's a pound the world around" but that is only true in the USA, in the UK a pint is 20 ounces. Talk about parochial!

Contrary to popular belief Canada is not realy metric, it is only officially metric. I have lived here all of my 53 years and it is metric for visitors as the speed limit and gas and milk(not butter 454grams =1 lb) are all metric but materials to construct any thing are all in inch sizes, so when you design something if you want to not wait months for the material to arrive, you must use inch sizes. Going all metric would help as all of our new engineers have to learn ft/lb, psi....

Calling us backwards because we didn't want to spend so much money and resources to "be like everyone else" is a bit harsh.

And I remember growing up in the '70s and the push to convert and the resistance it received. I learned metric in school, and I never did fully memorize all the english measurements (I know a pint is less than a gallon, but not the ratio).

The solution: If we want to have progress, the government only needs to:

1) require gas be sold in metric (and hopefully in cost units available in the US, no more 9/10's of a penny).

2) require work done on gov't contracts be in metric

3) require schools to stop teaching English measurements.

Soon we'll have critical mass and this problem will just fade away on its own.

As for time, the second is a metric standard, and minutes and hours are non-standard. However the "day" is non-exact, and there is currently a big issue with increasing numbers of leap-seconds, which cause systems like GPS some pain. The "year" is even less exact, with leap-yeaars every four years except for exact centuries but not when it is divisible by 1000 ... so 2000 was an exception.

Seconds are just fine, because the significant human-convenient time divisions are non-integral, and decimal doesn't work.

The French tried metric time after the revolution, but it never caught on. I don't think anyone said we had to use base-10 for everything. I use hexadecimal almost every day for programming and it makes bits and bytes easy to decipher. And I use octal and binary. That said, an early manual for the 8008 microprocessor did list op codes as decimal numbers. That changed quickly.

I didn't know there was such a thing as metric time, Jon. Upon checking it out, I found there is such as thing as metric time based on seconds, with terms such as kiloseconds and milliseconds: http://en.wikipedia.org/wiki/Metric_time

I have been a machinist and have a few machinr tolls at home. I participate in several machinist forums and have seen this discussion come and go over several years. As long as one understands the system one is working ai and how it relates to the other system there is little, if any, problem. Sure, The Brits and the Americans still work with inches and the rest of the world works with meters. We can both make parts that are completely interchangeable with no extra effort. The arguments generally come down to - your system is wrong because it isn't my system.

Consuder the cost of retooling. If I was active in a machine shop my measuring tools alone would come to approximately $3000.00 to replace. Quite a hit to the individual craftsmans wallet and they aren't paid all that great anymore.... And then the companies that have thousands of dollars worth of tooling that would have to be replaced. And for what? so we could say we made it to 25.40MM instead of 1.000"?

The anecdotes that are used to justify metricization are more examples of poor communication and poor practice. The satelite and mars probe problems were more likely caused by a rushed production and testing program and revealled a need for better quality control. Rushed work in metric can still come out as crap. and chromed crap in metric or english is still crap.

When the Confederation of British Industry (CBI) surveyed its members about metrication in 1980 — after 15 years of British metrication — they found that

"... the extra cost of continuing to work in dual systems of measuring was around £5 000 million every year."

This cost must be a huge drag on competitiveness. Even if the USA does not like metrication internally, many foreign markets will demand metric products, and manufacturers have a choice of dual standards of losing buiness.

To an individual, an additional or new machine is an unwelcome cost, but if everyone is replacing old machines over a period, the simplification of uniform standards must be a big benefit. There is nothing to stop a lathe from being set to 25.4mm to cut 1" for old legacy compatibility.

The idea of metric conversion is much easier than the application. Try and purchase Metric paper for your printer, then try and re-adjust your printer to use it. Architectural building drawings are still mostly in Feet and Inches. When was the last time you found a metric drill index? They are all SAE with the metric value in parenthesis. All this is after almost 50 years of trying to change. There are not enough market forces to demand a change to metric and depending on the government to oversee this dooms it to failure before it even starts. Saying the US and Britain are the only 2 countries using this backward system is perhaps a bit elitist. I have no hard data, but I think these 2 backward countries do contribute a significant percentage of the worlds industrial output. Change is happening slowly. Maybe in another hundred years we'll all be metric but I wouldn't count on it.

The superiority of the decimal system over fractions was obvious to me as a high school student well over 50 years ago, and it still is! Anyone who can't see that must not do any calculations beyond addition and subtraction.

Yes, I too have lots of measuring and machine tools that were made and calibrated to non-metric standards, but that is mosly due to the lack of intelligent leadership in the past. Fortunately the increasingly affordable electronic measuring tools can be changed with the press of a button, so the final changeover would be less costly than in the past.

All we need is intelligent leadership to do it! OK, where do we find some intelligent leadership?

Hi, CPDick. I'm in the same position. My mini-lathe and milling machine have inch graduations but I could retrofit them with digital scales and use English or metric units. When my son and I finished a basement room we used a metric ruler because it was easier to give dimensions in centimeters; 37.6 cm vs "18 and 3/4 and a bit." Stanley makes a nice 8-meter retractable ruler (33-428) that includes inch and foot markings. Of course we had to use the inch scale to lay out studs on 16-inch centers.

Saying move to metric does not solve the lack of metric standards being used in industry in other countries.

There can be 4 different pitches for several thread diameters, different hex sizes for the same bolt diameter and nut depending on the country of origin. Several of the metric fastener diameters require a pitch gauge to tell the difference between coarse and fine thread. The difference between coarse and fine thread in metric fasteners does not equal inch fasteners when looking at maximum pull capacity. In a product where fasteners are used in tension the choice of thread pitch can have a significant effect on space and cost of manufacture. NC and NF inch fasteners are enough different that you seldom use the wrong nut on the bolt.

Metric o-rings need an international standard today. If you tried to stock every possible metric o-ring it would require over 2,000 different part numbers. The difference in diameter on some of the o-rings is so close it is difficult to measure and there is not a good reference for groove measuring information. So when you work on a metric hydraulic cylinder it can take substantially longer to order the seals than an inch size cylinder. Metric rod and piston seals are even less standardized between countries.

Several manufactures cannot even use the SI standard for pressure. Bar and kg/cm is a common term used for pressure not Pascal, the SI unit.

Try buying metric steel at the same price per pound as inch size here in the states. We as a small manufacture continue to adopt metric as quickly as affordable.

I can easily accomodate Metric measurements, I use both daily. I'm not satisfied with the Metric fastener standards at all. I see very little difference between metric 'coarse' and 'fine' threads, those words are ambiguous. English fasteners that have threads that mate (ie not wood screws) are specified by size, threads per inch, and length. 6-32 by 1" tells the whole story, thanks. BTW, the standard for Printed Circuit Board design remains in "mils" which is .001". Almost all designs convert to this standard before release to manufacture, even if the parts are specified as "metric"

My metric screw gauge includes both fine and course threads. so it's easy to tell one from the other--when I have the gauge handy. Otherwise, not so. I visited my in-laws recently to replace an outdoor lamp fixture. I needed longer screws to hold it in place and used a screw gauge in a home-supply store and one of the screws for the new fixture to identify the thread size. The gauge showed a perfect fit in one of the threaded metric gauge holes, although it looked like a 6-32 screw to me. The screw would not go into the 6-32 hole, though. Turns out the screw WAS a 6-32. Someone had bunged up the gauge. Well, another trip to the store.

Hi, Ann. Same here--two sets of wrenches and also two sets of Allen wrenches. Thank goodness we can still still use slotted and Phillips-head screwdrivers in metric and English fasteners. Except in Canada where they love the square Robertson-head-drive screws. Nationalism, I guess. Robertson was a Canadian. Wikipedia has a good list of screw drives: http://en.wikipedia.org/wiki/List_of_screw_drives.

Ahhh.. the Robertson!. It was the greed and stubborness of Henry Ford that prevented an intelligent long-term deal with Robertson (Ford was already saving a lot by using those screws, but he wanted more). Robertson fasteners have a lot of qualities, but few people have used them. Can be torqued tremendously without rounding either the hex head or the "Allen" wrench; you can hold them very securely on the end of the Screwdriver w/o letting them fall inside the engine bay or worse, they are a joy to use single handedly. It is not only a pitty, but a shame that this truly excellent design was NOT used in cars. Car maintenance and Hot rodding would be much easier with them! I'm happy using them for high quality speaker cabinet construction and to build electronic chassises where a single slip of an screw driver would mean an ugly scratch on the front panel; and the joy of using them completely justifies their price.

Robertson-head screws and tools prove difficult to find here in the US. I have a set of screwdriver bits and use them mainly for screws in electrical panels. I suppose those panels and circuit breakers have customers in Canada and the US. For an interesting and related book, see:

"One Good Turn: A Natural History of the Screwdriver and the Screw." Amazon has it in paperback for about $US 6. --Jon

p.s. It would help if this darn blog-post tool provided more control over fonts. Sorry about the big bold characters.

Jon, I agree about the ability to use Phillips and slot head screwdrivers on everything. Those are probably the two tools I use most around the house. I've encountered Robertson screws occasionally, but find it harder to turn them (even using the correct tool!) since the geometry takes more torque.

I believe the USA already has. I have found using both metric and imperial measurements can be helpful for different applications. Sometimes using one or the other give the perfect fit. For example, no imperial/english standard size is close to 0.700", but the metric 18mm is almost perfect. So, I would go with the standard 18mm for parts, sizes, etc.

I like the fact that the USA has both in practice. It give us the ability to choose.

It sounds like there are really only two countries that are not on the metric standard: USA and England/UK. The only argument for not switching is that it would be too difficult/costly. Difficult because we'd have to learn a new system. Costly because of the retooling costs. I think neither of these arguments are valid. One says that we are not smart enough to adapt, which is just not true. The other assumes the initial cost of changing (e.g., retooling) is the only cost to consider. How about the fact that metric fasteners cost more in the US because they are not as plentiful as english unit fasteners. That's a cost that hits me every day. So in that case, switching to metric would flip the demand (in theory) and there would probably be a better variety of fasteners as well. Moreover, I wouldn't have to pull out my calculator to figure out what 7/64ths drill bit is in decimal.

Bottom line, the metric system isn't that hard to learn and the cost is a one-time expense. The benefit is that we conform with the vast majority of society which may not improve the average American's life, but will definitely simplify mfg and design for engineers.

Hi, btwolfe. Many US companies already use metric units because the export markets demand them. So some tooling changes have already occured. We'll pay the cost at some time, so I agree, why not now? I doubt the change would seem as disruptive as some people think.

Jon, I retired from GE in 2005 and at that time we did just as you have suggested; i.e. use English and Metric dimensions. The metric dimensions were enclosed in brackets, [ ]. All of the CAD work accomplished for GE Appliances is done in India by a company called Satyam. One of the major reasons drawings and literature are in both systems is the need for a "global" presence. Even in the appliance business, GE has markets in the USA, Latin America, Asian and Western Europe. I still have problems going back and forth but as I read drawings in using both I have adapted somewhat to the "other" system. Like Ann, I have two sets of tools in my work room; one for the Kirby vacuum and one for my Toyota truck.

Under he first Jerry Brown term as governor of California he has the state go metric. We bought liters of gas and drove kilometers instead of miles. The next governor was George Deukmejian who reversed it back.

I agree that we should go metric but there are many idiots in this country that think this is a subversive foreign French plot for World government under the World Bank or who knows, maybe the Yale Yacht Club.

It's long overdue and will probably have to be introduced by the Republican Party in order not to be considered subversive (like the Nixon trip to China).

It's the political fringe that makes the most noise and now with the Internet the fringe is in high gear and amplified beyond belief.

There have been several high profile aerospace mistakes made by using two systems and getting confused. Several have involved rocket launches and even a Mars probe that didn't make it. There are probably thousands of such mistakes that are costly in terms of money and perhaps even lives that aren't reported in the press.

The US nearly converted to the metric system around 1920. Many technical publications from around that time were in the metric system. Now no. 100 years on the religious and political structure of the US will not allow such a change.

Seem like I remember the US trying to convert to the metric system when I was a child back in 19??. This was many many years after 1920 lol. I wasn't a driver but think I saw speed limit signs with both number systems displayed.

I totally agree that it is time to go metric. I work at a European company that is 100% metric. We do not carry spares of Standard bolts because all equipment (even equipment built in the US) is 100% metric. It was easier to adjust to the metric constraints than I thought it would be.

It seems like most of you are on the metric basndwaogn. So much is this going to cost? I hadn't read anyone mention it costs money to convert to metric. maybe I missed it. The highway system alone should cost millions. Every mile marker and tenth mile marker would need to be replaced and repositioned. And every exit would have to be renumbered. We've spent years changing sequencial exit numbers to match mile markers. And how about speed limit signs. There are no dual posted speed where I live. And replacing all the maps.

Look in 37 years I would think that every thing that needed to convert to metric has and evrything that didn't, hasn't. So what's the benefit in converting what's not metric to metric and is it worth the cost? We seem to be getting along just fine with a mixed system.

I used to relatively apathetic on this matter. Up until about a few months ago, it wouldn't have bothered me if we continued to primarily use imperial, but a switch to metric would make all those units learned in science classes all the more relevant.

'It (USA education system) teaches two systems of measurement in the schools and, the confusion from learning two systems aside, there is a cost to the time spent in teaching two systems. A full year of mathematics instruction is lost to the duplication of effort.'

We use a full year of instruction to teach two systems of measurement. That's a year that could be used to teach an entire subject. Most importantly, it's a year that could be used alleviate a widening gap between US students and their international counterparts, most of whom only have to worry about one system of measurement.

It has always seemed to me that a large impediment to "learning" the metric system has been an obsession with mathematical perfection: we try to teach that a millimeter is .039370078 of an inch, and everyone glazes over. At the same time, nobody knows EXACTLY what an inch is, we're comfortable with it because we know close enough for our purposes.

I think it would make it easier if we could either learn metric units independently, without reference back to imperial units, or else relate them in easy-to-remember general terms that are good enough for practical purposes: an inch is about 25mm, a gallon is about 4 liters, a mile is about 1.6 km... people whose tasks require more precise knowledge will acquire it in any case.

As for manufacturers converting over, there is cost involved: we have existing stocks of US fasteners that can be hard to distinguish if accidentally mixed with similar metric ones, we have shorthand default tolerance systems on our prints that are based on the units being expressed in inches, we have standardized material stocks in inch increments. The structural difference between a piece of inch-size steel tubing and its closest standard metric neighbor can be very significant and require substantial redesign of the product that uses it. The cost of the change may not be great, but in business everything comes down to cost vs benefit: if 99% of your customers are in the USA (the size of the US market and the physical size of the country make this fairly common, unlike many other countries whose manufacturers can hardly operate without exporting) and are either neutral or prefer the US system, a business may not see enough benefit in the conversion to cover its cost.

The change will come ... but we've been saying this for over a century now (the US first recognized the metric system legally in 1866), and it hasn't come yet.

It was 32 degrees in the shade here today. Don't any of you give me the temperature at your place in farenheit. There isn't even a simple conversion factor. Have you noticed that datasheets give product dimensions in mm and archaic inches, but operating temperature only in Celcius ? Some things will always be measured in inches - here water pipes are always specified in inches, for some reason. Yes, you look silly with your pounds and gallons. Did anyone mention the Boeing 767 which ran out of fuel mid-fight because it had been fuelled using the wrong units?

This whole discussion is completely pointless, folks. There is absolutly no need to "adopt" the Systeme International (don't count on anyone but Americans' knowing what you mean by the "metric system") because back about 1860, believe it to not, the US Congress passed a law saying Americans could use the SI if they wanted to. The SI has been a ratified American standard for some time now and is covered (with a few mistakes) in ANSI SI 6 [? I might have the number wrong]. The kind of people who can benefit from the SI, can easily use it in their products...or not (excpet for getting that pesky lower-case, Greek mu to appear correctly in all media). There is no need to cram SI units down the throats of ordinary Americans. I too have no use for how many km it is from Harrisbug to Philly and I certainly have no need to know how many cm it is! There are a few things that Americans could learn about the SI. Firstly, it is an international standard so pronounciations are standardized too. Just like Carl Sagan used to inton, its "kilo-meter/metre" not "kuh-lom'-eter." And no, captial-K is not the multipoier for 1000; lower-case "k" is (captial "K" is the abbreviation for kelvin - which never takes a degree sign but celcius does). And there is no micorn; it's now micrometer (pronounced "micro-meter/metre" and not "my-crom'-eter"). The rules for pluralization vary from language to language, and some languages do not make this rahter pointless distinction at all. So SI 6 is in error when it specifies English pluralization conventions. The plural of "henry" is NOT "henries"l SI units are simply never pluralized (RPMs for that matter too). As for abbreviations, you have at least three choices for the abbreviation of liter/liter (both spellings are standard). The abbreviations for minutes and seconds are "m" and "sm" not "min" and "sec," sorry. While the micron is no more, if you are a phycist, your beloved angstrom is safe. And if you are an commercial airline pilot you are required to measure distance in nautical miles and altitude in feet (just thought that the metrication fanatics reading this would like to know that when they are a passanger on any country's airline, the pilots are usint Imperial units. YIKES!)

I lived in the USA for over 20 years and I have just returned to Australia which had a successful conversion to SI/metric in the early seventies.

There was a government mandate with a carefully considered plan and time limit. (The conversion was actually completed well before the time limit.)

There was no transition period where dual measurements were used. People just stopped using the ancient measurements. Road signs were converted in a single day. We bought our tomatoes in kg rather than lb, we drove at speed limits in km/h and that was it. Note that we never used hectograms like the Canadians. That is just weird. All food prices are per kg, not per 100g.

This is not to say that phrases like "six feet under" and "a mile a minute" suddenly disappeared from the culture to be replaced by silly metric equivalents. Even today people still talk occasionally in feet and acres.

It may be a bit surprising but the people who adopted the metric system quickest and loved it the most were construction workers. Their lives suddenly became much easier. No longer were dimensions on plans given as things like 13 ft 9 7/8 in. Instead that dimension would appear as 4207. Note the absence of units. It is always mm. Simple.

A corollary to that is avoid the use of cm in most cases. 4207 is better than 420.7 cm.

For those who love the old units, remember this. The US was one of the first countries in the world to use a decimal coinage, abandoning the British system of 4 farthings to the penny, 12 pence to the shilling and 20 shillings to the pound. Consider how much easier it is to add $4.70 and $2.85 than to add £2/14/3½ and £1/10/11¾. Would anyone even contemplate going back to that sort of system? Yet the US retained the 18th Century British measurements which are equally complex.

I have heard people say that the old British measurements are somehow more "natural" than metric ones. Really? How is the length of three barley grains laid end to end relate to everyday life? Yet that is what an inch supposedly represented. (Now it is defined as 25.4 mm exactly). Is a foot really the size of someone's foot? Certainly not mine, or my wife's or my grandson's. A meter, by contrast, is pretty close to the median height of the population (including all ages) and is arguably more natural than the foot. 100 mm is about the width of my hand (including the thumb) and a liter is the volume occupied by a box one hand width on each edge and whien filled with water weighs 1 kg. What, by contrast is a gallon? In the US it is 231 cubic inches and corresponds to the Queen Anne wine gallon. How natural is that? What is a pound? The weight of what? What is the relationship between a fluid ounce and an ounce weight? What is the difference between a dry quart and a liquid quart?

We all know from school days how far 100 m is. It is the distance between the start and finish line of a common and fairly short foot race. Make a square with that distance on each side and you have a hectare, the common land measurement. It is easy to visualise. Now picture an acre. What exactly does that look like? It was supposed to represent the amount of land a horse could plough in a day. Do you have a horse and one of those single-furrow ploughs?

Yes there are costs associated with conversion. However for the most part they are one-off costs but failing to convert incurs recurrent costs in terms of dual tooling, difficulty in penetrating world markets and unnecessary complexity in education, construction and everyday life. Furthermore as others have pointed out, the failure to effect a speedy conversion actually increases the costs because materials in metric sizes are in short supply and hence more expensive.

Australia did it. New Zealand did it. South Africa did it. We now reap the benefits. It is about time that the USA did it too.

The remark about inflating tires makes the point, but not the way it is intended. The basic unit, the pascal, is a very small, mostly useless unit. So metric-descriptions for hydraulic pressure seem to use other units. Likewise, measurements of length is most often in cm or mm, because the basic unit, the meter, is a bit bigger than our yard. The yard approximates to a running step, making it good for football announcers. For all of my design work over the years I have used inches, and decimal fractions thereof. Then there is no confusion for the folks using the drawings.

For hydraulics, pressures in PSI multiplied by cylinder diameter give forces in pounds, with no conversions to other units needed. Consider: 250kPa x 100cm2=?

Now for bolt sizes the strength ratio between inch-sized bolts is far more useful than it is for metric bolt sizes. That is because many design engineers select bolts based on the load that they need to carry. While the metric math is simpler, the sizes are not as intuitive.

Really, all that we would have needed to do was to get rid of the standard fractional system of measurement and moved on to decimal fractions, and our system woulde have been so very much simpler.

@William K: Multiplying a pressure in kPa by an area in cm² gives you a force in units of 0.1 N (1000 · .01²), so you just have to move the decimal point one place to the left. That's a lot easier than dealing with conversion factors of 12 (inches/foot), 16 (ounces/pound), etc. And multiplying pressure in MPa by area in mm² gives force in N directly.

I never ever use units of ounces or feet. Mixed units of measure are an invitation to errors, and should be avoided for that reason, if for no other. Certainly those conversions are quite inconvenient, which is always quoted by those touting the metric system, but simply avoiding mixed units is very simple and very effective, and should have been done 50 years ago.

@William K: I've seen torque given in inch-ounce, inch-pound, and foot-pound units. For some reason, I've never seen foot-ounce units, but I don't doubt that they exist. This causes no end of confusion.

I've also heard that the correct terminology for torque is actually ounce-inches, pounds-inches, and pounds-feet. This is supposedly in order to distinguish energy in foot-pounds (a scalar quantity) from torque in pounds-feet (a vector quantity). Of course, nearly no one uses this "correct" terminology.

At any rate, the "correct" terminology seems kind of silly, since multiplication is commutative, and there is no difference between multiplying 1 lb by 1 ft and multiplying 1 ft by 1 lb; it only matters whether you take the scalar (dot) product or the vector (cross) product.

In SI, torque is in newton-meters, and energy is in joules (1 J = 1 N · 1 m). This is at least more credible than the idea that, by changing the order of the words, you can distinuish a dot product from a cross product.

By the way, although I seem to be defending the metric system, I'm personally much more comfortable with inch units, and prefer to use them wherever possible. This is just a matter of custom and familiarity, more than anything else.

For some reason, I don't need to make a conversion in my head when I'm talking about liters, meters or kilograms. Newtons, however, is another matter. When someone expresses Newtons to me, I absolutely have to sit down and convert it to pounds-force. I just don't have an intuitive reaction when someone says, "This is 50 Newtons."

Meters, liters, kilograms, and degrees Celsius come more easily than others based on many years in the lab working with those units. I can't recall the last time I thought about any Newtons except those with the fruit filling. Just not a unit I commonly come across. The IEEE published a good unit-conversion book, "Metric Units and Conversion Charts," by Theodore Wildi that helps simplify moving between measurement units.

I usually end up multiplying by 0.22, Dave, but the number seldom sticks with me. I constantly have to go back and look it up, whereas I don't seem to need to do any mental calculations to evaluate a centimeter or millimeter or a kilogram. I guess it's a matter of teaching an old dog a new trick.

I have indeed come across the Robertson scres, but this is the very first time that I have heard thier name. Also, from China we get them made to also accept a Philips driver, and even a straight driver. And when thier forming die wears out they send screws that are hard to use with any type of driver.

The biggest failure of metric unit hardware is that it is not sized in practical proportions, meaning that the strength ratios are strange, and for thread pitches, it seems that they are sort of insane. I recall small metric screws with pitches of 1.2 and 1.5, and then some other pitch as well. That makes much less sense than our more reasonable 4-40, 6-32, 8-32, and 10-32 screw thread sizes. THose sizes have a useful strength ratio, each about twice as strong as the previous size.

It won't be too much longer and hardware design, as we used to know it, will be remembered alongside the slide rule and the Karnaugh map. You will need to move beyond those familiar bits and bytes into the new world of software centric design.

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